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As rage suggested in a previous post (puzzled)I hooked the 6v6 tubes in the schem above in triode mode by tying grid 2 to the plate with a 150 ohm resistor and I removed the feedback loop from the secondary to the cathode and did not make the hookup from grid 2 to the opt. The opt I am using does not have ultra linear taps. Everything else is per the schem.
I have one channel bread boarded and I am getting music out the other end but it is very distorted. I measured the b+ voltage and it is at 325vdc, and currently I have 300vdc at the plates of the 6sl7. Trying to figure out what voltages I should have where to be able to check them. Since there is only the b+ voltage given on the schem do I have toput a resistor in series with the center tap of the opt to measure the voltage drop so I can calculate the current and then use ohms law to work my way back through the schem, or is there an easier way to do it? Oh, my psu is not the same as in the schem, but it is similar and tube rectified.
Thanks
Follow Ups:
Yep, putting the 1k resistor from the cathode to ground was the answer. Thanks a bunch everyone! Now I can check everything else out.
Vinnie
Since the voltage on the 6SL7 is at rail, you need to make sure the top half of your 6SL7 cathode resistor reads 1k. If you disconnected the feedback,it won't work because the 1k resistor is being grounded thru the OPT transformer secondary.
Edit.
I see the 100 ohm and that takes care of the lower triode's resistor but make sure the upper triode reads 1k from cathode to ground.Also make sure the 470k grid resistor is grounded.
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Edits: 11/24/14 11/24/14
Are you saying the same thing as Ralph did below, that I need the 1k resistor and the cap from the cathode of the 6sl7 to ground?
I just read what Ralph wrote and yes,I am saying the same thing.The 6SL7 will not conduct unless you have a cathode resistor going to ground which in this case is also a feedback resistor. If you want to eliminate the FB loop for shits and giggles,just ground the 1k resistor on the side going to the transformer secondary after you disconnect it from the secondary of course.
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Edits: 11/24/14 11/24/14
That the current path for the 6SL7 was broken?
Install a 1000 ohm resistor to ground and it will play.
Do you mean install the 1k resistor and cap back in from the cathode of the 6sl7 to ground?
Edits: 11/24/14
I believe just the resistor, to complete the circuit, the bypass cap (100uF) is still there. The 1000pF is only for the feedback loop so not necessary.
Dave
yeah sorry I missed that. to remove feedback you'll need to tie the cathode of both tubes to ground with a resistor.
ok, but install it from where to ground?
That's where it goes when the feedback is in place (we can assume the secondary of the transformer to be negligible).
That bypass cap won't make a very good DC current path :)
If your 6SL7 has 300v on the plate, and the B+ is 300v, it means the 6SL7 isn't drawing any current. Check for correct cathod voltate on the 6SL7 and trace to problem from there. I'm guessing plate should be at 200v (100k at 1ma aprox) drop from 300v B+.
You only need to look up the typical operating conditions shown in the datasheets. That will tell you what voltages to expect and how much current should be flowing through the tubes. If it's distorted, you'll likely find a voltage or current that's way off. It won't be a subtle difference.
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Buy Chinese. Bury freedom.
Cool. Thanks!
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